Hi, friend!
I was faced with the same problem. Not able to run iClone v6.21 PRO and iClone CharacterCreator v1.21 under Windows 10. iClone 3DXchange v6.21 Pipeline works normally.
I wrote to support, but after reading the forum I realized that I most likely will not beable to help. Then I began to look for a solution myself.
I must say that under Windows 7 the problem remains.
I wanted to buy another video card, but its price is 500 dollars forced me to be creative. I live in Russia, and in our country there is an opinion that many large corporations are releasing updates to their products to gradually reduce their performance and functionality. This encourages the user to purchase more fresh devices.
So I found a website where an archive of Nvidia drivers. Here's his address:
http://www.3dnews.ru/220023
The site is in Russian, but read there is nothing. The names and versions of drivers, no one translates into another language. ))) However, you can always find on the Internet a lot of other sites that archive drivers.
I can say – with driver version 355.98 iClone 6 already does not run. But, if you install the 340.52 driver, iClone starts up and works fine. Just don't update it. Maybe with your hardware the program will start to work on later version. You can experiment, and I'm a little tired and don't want. ))
I can say that this only applies to Nvidia video driver. The other driver in the Nvidia installer package (such as HD Audio and 3D Vision) may be later.
Although, I can't claim that all the fault of Nvidia. Maybe that Reallusion may not work correctly with the new Nvidia drivers. I think the truth we will never know.))) However, a solution has been found. We can rejoice!
Good luck!
P. S. If you don't update the firmware on the phone, it will work one hundred years.))))